1. Field of the Invention
The present invention relates to a device and a method for detecting overheated parts which can cause a catastrophic failure by measuring contents of gaseous decomposition products contained in hydrogen gas which is used as a coolant.
2. Description of the Related Art
Overheating can be occurred in case there is abnormality such as deterioration of insulating material, windings shorted, damaged strands, and partial discharge within a generator or a motor in operation. And adjacent materials such as epoxy, enamel, paint, varnish, insulating material, air, etc. are decomposed by the heat, which produces particulate or gaseous decomposition products.
These produced decomposition materials are contained in cooling gas (hydrogen or air). Thus, occurrence of abnormality can be informed by detecting particulate or gaseous decomposition products contained in the cooling gas of a motor or a generator.
The size of particles produced by decomposition of the adjacent materials such as epoxy, enamel, varnish, and insulating material is 0.001˜0.01 μm or so. Currently, the only worldwide product used for monitoring hot spot in generator is GCM, Generator Condition Monitor (also called Generator Core Monitor) which monitors by detecting particulate decomposition using ICD (Ion Chamber Detector) sensor. GCM was developed by GE (General Electronic) in US and has been sold by GE and Environment One Corporation.
ICD detects by charging particulate materials using radiation source (thorium 232). The output of sensor is decreased as the concentration of particulate material is increased. In normal condition, the sensor output is adjusted to be about 80% of full scale. And an alarm is issued if sensor output goes below 50%. GCM have had frequent invalid alarms due to causes not related to generator overheating such as the intrusion of oil from generator sealing oil system and moisture from hydrogen cooling system into generator and low sample gas flow. Thus, it is true that the reliability of the system is low. Although a trap can be installed in the upstream of the detector to remove oil, it also removes the particles together, and decreases the sensitivity of the sensor. Many devices of this type have installed on a number of generators in the country. The devices stopped or removed from the system are increasing due to frequent malfunction.
On the other hand, if there is a hot spot due to abnormality within generator, various gaseous decomposition products (VOCs) are produced. Those produced gaseous decomposition products (VOCs) are shown in Table 1.
TABLE 1Gaseous decomposition products (VOCs) producedwithin generatorgaseous decomposition products(VOCs)1.Heptane2.Dioxane3.Toluene4.Octane5.Xylene6.Benzaldehyde7.Trimethylbenzene8.Decane9.Methyldecane10.Methylphenol11.Undecane12.Benzothiazole13.Bisphenol-A
Those produced gaseous decomposition products (VOCs) appear in different amount depending on the size of abnormality, thus abnormality of generator in operation can be determined according to concentration of gaseous decomposition products (gaseous molecules).
In detecting gaseous decomposition products, PID (Photo Ionization Detector) sensor or semiconductor type sensor can be used. PID sensor includes a light source emitting light of short frequency (Ultra Violet), and two electrodes. If the light of UV is irradiated to gaseous molecules, some of molecules are being ionized, i.e. converted into positively charged ions and negatively charged ions. Positively charged ions are attracted to cathode and negatively charged ions are attracted to anode, which makes current flow.
In this process, the flowing current is proportional to the concentration of gaseous decomposition products, thus the concentration of gaseous decomposition products is measured. In a PID sensor, the oil contained in the gas sample (cooling gas introduced to sensor) can pollute the sensor and too much moisture can decrease the sensitivity of the sensor, so they have to be removed before introducing to the sensor. Also when an alarm is issued, it is necessary to check whether warning is due to the actual situation or malfunction of the device.
As a specific prior art, the technology disclosed by Patent Publication No. 10-1209428 dated Nov. 30, 2012 ‘An apparatus for generator condition monitoring using VOCs sensor’.
In referring to the prior art illustrated in FIG. 1, the prior art comprises a preprocessing module 1 for taking some hydrogen gas (a sample gas) and removing moisture or oil in the hydrogen gas, a filter 2 for removing particles larger than 0.001 μm, flow controller 3 for introducing a certain amount of a gas into the sensor, gaseous decomposition products sensor 6 sensitive to gaseous decomposition products contained in a hydrogen gas, and a signal processing module 7 for issuing warning when the concentration of gaseous decomposition products exceeds the control standard value. And in the detection of gaseous decomposition products it is possible to remove the moisture or oil in a hydrogen gas before introducing the sample gas to the sensor. Thus, malfunction due to moisture or oil can be prevented and this kind of hot spot monitoring system can be more reliable. The oil and moisture which contaminates the sensor or decreases the sensitivity of the sensor are removed by filter and moisture trap respectively, which means the prolonged life of sensor and high sensitivity. Appropriate repair plans can be established and reacted depending on degree of abnormalities by monitoring continuously generator conditions. Thus, it can contribute to stable power supply by preventing unplanned shutdown and reduce maintenance costs.
However, the prior art is configured to have a means to prevent the reason of malfunction in advance, water leak can occur by corrosion of the system since water is used for cooling in the preprocessing module 1. In case the temperature of water is high (in summer), removal of oil or moisture in the actual hydrogen gas is not enough by degraded cooling effect and thereby gaseous decomposition products sensor is contaminated or performance of the device can be degraded by degraded sensitivity of the sensor. Thus, in case an alarm is issued, there is the limit to make operator's decision difficult since there is no means to verify whether warning is due to the actual situation (occurrence of overheated parts), or abnormality of the device.